A sodium-sulfur battery (hereinafter referred to as “NaS battery”) is a battery that operates at a high temperature. Therefore, the NaS battery is used with a heater that heats the NaS battery, and is operated in the state of being kept at a high temperature.
Patent Document 1 relates to control of a heater that heats the NaS battery. Patent Document 1 refers to a problem with a conventional technique, which is a decrease in released power due to power supply to the heater (paragraph 0007). Further, in order to solve this problem with the conventional technique, Patent Document 1 refers to solving means such as decreasing a set temperature of the heater during a period after completion of charge until start of discharge (paragraph 0015).